Besson and Tasioulas have coordinated the contributions of 33 authors in compiling an impressive collection on conceptual issues in contemporary public international law. Taken overall the chapters illustrate the importance of a more philosophically informed approach to international law and therefore the significance of the interface between legal philosophy and international law. The most stimulating of the contributions are those which provide fresh insights from outside international law (for example, from political philosophy) on long-standing problems in international law.

The general orientation of the collection is towards normative considerations in international law—focusing on values and on ethical criteria. The significance of such considerations is strongly communicated in the collection. One effect of the collection should therefore be to stimulate adherents of the analytic or positivist camps within international legal theory to take a fresh look at their own conceptual foundations. The notion of ‘state consent’ is a case in point. It is argued throughout the collection that State consent (with its baggage of the ‘will’ of States) is a feeble construct in the explanatory repertoire of international law, although progress with the articulation of alternatives is modest.

The book is organized into Sections usually containing two chapters, either addressing similar topics in complementary ways or with the second responding to the first (at least in part) so that a sense of dialectical engagement emerges. This generates a lively product (rather than a dry ‘Handbook’) but also delivers the message that the contribution of philosophy is often methodological as much as substantive, in highlighting the importance of robust debate, and modelling such debate. In general this design succeeds, as exemplified by Tasioulas' response to Buchanan (on legitimacy) and Howse and Teitel's response to Pogge (on the impact of international trade law on world poverty). In both cases the responses improve the precision of the original and significantly enhance the analysis of these important issues. However, in some other cases this paired design generates textual repetition and excessive citation in the second (response) chapters and excessively focuses debate on details of authorial expression in the target chapters. Occasionally the debate format threatens to degenerate into the clubby (Luban) or the strident (Zolo).

Some of the most effective Sections such as that by Kymlicka and Waldron work by complementarity rather than by conversational engagement. Kymlicka compares and contrasts rights of ‘national minorities’ with rights of indigenous peoples, while Waldron skewers the conceptual inadequacies of ‘self-determination’ (also offering a path forward). The same can be said of Paulus and Regan in their carefully argued, complementary chapters on international adjudication. By contrast the ‘triple-barrelled’ Section VIII on human rights (chapters by Raz, by Griffin and by Skorupski) is disappointing, with issues somewhat underworked in relation to public international law. Raz' tone is tentative and exploratory when a more substantive contribution might have been anticipated. The same may be said of the Endicott–Cohen Section VI on sovereignty. Here the engagement with public international law seems insufficiently informed. In his contribution on international democracy (paired with Christiano in Section III) Pettit is more successful in terms of linking political theory (republicanism) with public international law.

Some authors are more successful than others at balancing the more general survey aspects, such as historical overviews of particular topics with the more focused, grappling with defined issues). Both chapters in the section on international responsibility (Crawford and Watkins; Murphy), for example, succeed on the balancing criterion. But the introductory chapter by Kingsbury and Straumann sets itself an impossible task in respect of coverage, and Buchanan's chapter on legitimacy remains at the level of the general and preliminary.

On the sources of international law, Besson sets out to develop a democratic and positivist account with which to replace the current orthodoxy with its questionable grounding in State consent, as provided in the Statute of the International Court of Justice. For Besson the ICJ typology of sources is ‘largely obsolete’ which seems slightly over-reaching. Besson's new account, which is no more than sketched, includes reference to a (quasi-Hartian) rule of recognition and to norms such as a ‘duty to constitute an international legal order.’ Space is sufficient for Besson only to hint at, and not to explain, how these rules and norms might interrelate and how supposed hierarchies of norms and of sources interrelate with the democratic process. There appears to be the danger of the proliferation of normative claims. For example, Besson's argument concerning hierarchies of international legal norms refers to ‘the degree of … normativity’ and to ‘material hierarchies of norms.’ Both terms call for more rigorous development than Besson provides. Lefkowitz's paired contribution on sources explores a rule of recognition in more detail than Besson's. But to some extent Lefkowitz's account replaces State consent with consensus and shared belief among States, thereby begging certain questions concerning the ‘volition’ of States (to use Tasioulas' helpful term).

In common with several other contributors, Lefkowitz finds how difficult it is to give a brief and accurate analysis of customary international law. Little progress is made with this thorny topic anywhere in the collection despite numerous short forays into the thickets. The same may be said of jus cogens norms which are referred to by several authors but nowhere carefully examined. There is a sense that for some authors the technical detail is someone else's problem, an attitude also conveyed by the somewhat casual use of the term ‘Westphalian’ by many authors, as if that term had any stable content. Progress is going to be made by those scholars who are able to grasp both technical details and bigger pictures within international law.

There should now be no doubt that philosophy of international law is a valid sub-discipline comprising a range of contested approaches, claims, and intellectual affiliations. As the editors remark, a wholesale scepticism over the conceptual validity of international law—the holus-bolus spurning of international law's claim to be meaningfully lawful—does not survive scrutiny. This does not of course preclude the validity of more nuanced forms of scepticism such as emanate from post-colonial, feminist or postmodern quarters. At the same time it is unfortunate that the editors appear to endorse the orthodox view that municipal legal systems are ‘more highly developed’ than international legal systems, given the question-begging character of that comparative claim. Indeed as the editors propose, scholarly contributions that are adequate to the complexity of public international law often prove to be significant contributions also to public law in the municipality, despite the greater familiarity of the latter. In many ways public international law might be said to be the leading intellectual edge of public law. Certainly this collection makes such a claim plausible.